A railroad engineer needs to know the condition of the track in front of him, both as to whether it is occupied by another train, and as to whether the track itself is in condition to support a train. Considerable work has been done to transmit electrical signals along the rails between trains and transponders located in the track bed, so that the location, composition, and speed of each train can be continuously monitored by all the trains and by a centralized traffic control office. While such a system reduces the possibility of collisions between trains, it does not reduce derailments due to failure of the track itself.